1. Field of the Invention
The present invention relates to a method of measuring gonio-spectral reflectance factor. More particularly, it relates to a method of measuring, by a goniospectrophotometer, a gonio-spectral reflectance factor available for a database of colors of coating for rendering a three-dimensional computer graphics image.
2. Description of the Related Art
An analysis of a process in which an emitted light is reflected, transmitted, scattered and interfered on the surface and/or inside of an actual object and finally reaches to a receiving instrument or a receiving organ has been recently advanced. A technique of rendering a highly-fine realistic image in accordance with a gonio-spectral reflectance factor obtained by colorimetry of a coating plate is being advanced based on the approach for three-dimensional computer graphics using knowledge of these optics and colorimetry has been developed. This technique allows a color effect to be identified on a display when an object is coated with an actual coating and thus expected to contribute greatly to a design work, a work of developing a coating material, or the like. The term colorimetry means the measurement of a spectral reflectance factor for many wavelengths in a range of visible light wavelength.
The gonio-spectral reflectance factor has the parameters: a wavelength .lambda.; the direction of incidence of the light on the specimen surface; and the direction of reflected light from the specimen surface. This gonio-spectral reflectance factor is typically obtained by the use of a goniospectrophotometer, changing a viewing angle at which the light reflected from the specimen is received and then measuring the spectral reflectance factor at each viewing angle.
In the implementation of the colorimetry, the conventional measuring method is that a viewing direction is regularly changed in such a manner as step by step change by constant inclination since it can easily cover every direction. That is, the viewing angles are set at predetermined intervals, and then parameters determining the viewing direction are changed by appropriate amount. The measurement is done sequentially with the viewing direction being changed step by step in many directions. For example, the reflected light generally undergoes the colorimetry at each step, while the viewing angle. which is defined as the angle formed between the reflection direction and specular direction in a plane of incidence, is sequentially changed step by step by a predetermined increment angle.
For forming the highly-fine realistic rendering image in accordance with actual colorimetry data in the three-dimensional computer graphics, the gonio-spectral reflectance factor measured in every viewing direction is required. That is, preferably, the reflectance factors of the lights having as many wavelengths as possible and as many directions as possible are gathered in order to reproduce a reflectance factor distribution of the actual object. Thus, for gathering the colorimetry data, the colorimetry is implemented in very many viewing directions, e.g., in about several thousands to about ten thousands viewing directions by using the goniospectrophotometer. However, the more an amount of data is, the more difficult the gathering of the actual colorimetry data is.
For instance, about two to three days are typically required for subjecting one specimen, i.e., one surface color of coating to the colorimetry. Much time and considerable efforts are consequently needed for subjecting many surface colors of coating to the colorimetry. This is a bottleneck in the creation of a database of colors of coating for which about tens of colors to about hundreds of colors are generally needed and it is also hard to supplement new data of surface color of coating into a database.
Moreover, the colorimetry data inevitably becomes large in scale and hence the database requires a large storage capacity of a computer. This is a disadvantage in ensuring a processing speed and a storage capacity of a computer when the data is processed by a personal computer.
Thus, the rendering is actually performed by the use of a limited number of colorimetry data by taking into account both of the processing speed and the storage capacity of a computer. In this case, some partial viewing directions such as about 1/10 to about 1/tens of all the possible viewing directions are selected from all the viewing directions that can be measured by the goniospectrophotometer (i.e. about several thousands to about ten thousands viewing directions) by selecting the viewing directions regularly at each of angles spaced at one or plural predetermined interval(s). However, it is difficult to obtain information on the spectral reflectance factor needed for the rendering with no sacrifice in the fineness and the reality. Even if the viewing angles are sparsely or densely spaced depending on a region to be measured, the number of the viewing directions cannot be greatly changed.
Therefore, a method of easily creating the colorimetry database is not yet provided.
Thus, an object of the present invention is to provide a method of measuring a gonio-spectral reflectance factor to establish a gonio-spectral reflectance factor database available for a personal computer by which a highly-fine realistic three-dimensional computer graphics image can be formed in a reduced hours of a colorimetry in fewer viewing directions compared to the conventional method.